Perennials are among the best plants to grow in the garden. Unlike annuals, they come back every year, are easy to establish, and have lower maintenance requirements. Established perennials, which by nature grow larger every year, need to be divided to help control their size, to revitalize them, and also as a method of plant propagation. The fall is the best time of the year to accomplish this task.

How do you know if the perennials in your garden need to be divided? During the growing season, observe the plants for reduced flowering, stem dieback, dead centers in the clumps, and a general unhealthy appearance. In overcrowded plants, the roots will be growing in a thick, tangled mat. If the plants are healthy in appearance, they do not need to be divided unless new plants are desired.

The best time of the year to divide perennials is during the fall after they have finished blooming and have begun going dormant. Most perennials, on average, need to be divided every three to five years. Some, like chrysanthemums and asters, should be divided every year while others such as peonies and bleeding hearts, seldom, if ever, need division. Some perennials, such as Lenten roses, should never be divided since once established they are difficult to transplant.

A day or two before dividing the plants, water them thoroughly. The best method of dividing perennials is to use a shovel and dig down deep on all sides of the plant. Pry underneath the plants to lift them out of the ground, shake off the loose soil, and then remove the dead stems and leaves. Place the clump into a wheelbarrow, and then use a knife or pruners to separate the underground structures into individual plantlets.

Perennials have different types of root systems which determine the method of division. Ones with spreading roots, such as black-eyed Susan and garden phlox, have roots that lack a distinct pattern in their growth. They should be divided into smaller clumps each having a few viable shoots. Tuberous roots, which are the potato-like structures on plants, such as canna lilies and dahlias, should be divided by separating the individual tubers with a sharp knife. Each tuber should have a piece of the original stem and a growth bud attached to it. Those that spread by creeping stems, such as irises, (the stems growing underground are referred to as rhizomes and those above ground as stolons), should be dug and separated by pruners. Each division should have a few inches of the rhizome or stolon and a set of leaves attached to them. Clumping root systems, such as ornamental grasses, are divided using a sharp knife or a shovel to pry apart the roots to separate into smaller clumps.

Keep the divisions moist until planting. Prepare the planting area by tilling the soil, adding organic matter such as compost, peat moss, or top soil and then apply some low nitrogen fertilizer such as a 5-10-15. Plant the divided sections at the same depth they were originally growing. Then pack in the soil around the roots to eliminate air pockets. Cut back any top growth 6 to 8 inches off the ground. Apply a couple of inches of pine straw or pine bark mulch and water as needed.

Dividing perennials is beneficial in a multitude of ways and is necessary to have healthy, attractive plants. If you have any questions regarding dividing perennials, please contact the Gwinnett County Extension office.

Timothy Daly is an Agricultural and Natural Resource Agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010 or tdaly@uga.edu